Deflecting circuit



ATTORNEYS R. O 2 3 4 6 7 a 9 mm m m m .a. m m m w m F F F H F F F m m r4. J uu fi 1.1---- J J. DI PAOLO l I 22 F l g as I I I 4| l I I 45 June18, 1963 DEF'LECTING CIRCUIT Filed Nov. 24, 1959 United States PatentOffice 3,094,645 Patented June 18, 1963 3,094,645 DEFLECTING CIRCUITJolrn Di Paolo, Cedar Grove, N .J., assignor, by mesne assiguments, toFairchild Camera and Instrument Corporation, Syosset, Long Island, N.Y.,a corporation of Delaware Filed Nov. 24, 1959, Ser. No. 855,193 7Claims. (Cl. 3l527) This invention relates to a deflecting circuit for acathode ray tube, and more particularly to one that provides anundistorted display.

Cathode ray tubes draw visual displays by moving a spot of light acrossthe tubes faceplate. The spot of light, proper, is produced byimpingement of a beam of electrons on a fluorescent screen, the movementbeing caused by deflecting the electron beam so that its changingtrajectory produces different successive points of impingement. Toprevent the display from being either compressed or stretched at variousparts thereof, a given deflection signal should produce the same spotmovement, regardless of which part of the display is being drawn. Anundistorted deflection of this type is called linear.

Two types of deflection systems are widely used. The first is known aselectrostatic." In one type of electrostatic deflection system acapactance is charged, and the resultant voltage thereacross is appliedto deflection plates which thereupon form an electrostatic field ofvarying strength. This varying strength field causes the beam ofelectrons passing therethrough to be deflected. The second type ofdeflection system known as electromagnetic is one in which current iscaused to flow through deflection coils. This produces a varyingstrength magnetic field that deflects the electron beam.

Inherently, however, these two types of deflection systems, instead ofproducing linear deflection, produce a deflection that progressivelydeparts from linearity. Further increasing the nonlinearity, are theinherent system resistances, or those intentionally introduced into thecircuitry for various reasons, which cause the resultant deflection todepart even further from linearity. As a result, the prior art aboundsin compensatory circuitry that seeks to correct this nonlinearity.

It is therefore the principal object of my invention to provide animproved deflection circuit.

It is another object of my invention to provide an improved deflectioncircuit having extremely good linearity.

The attainment of these and other objects will be realized from thefollowing specification, taken in conjunction with the drawings, inwhich,

FIGS. 1-4 and 6-9 show various waveforms associated with electron beamdeflection; and

FIG. shows one form of my invention.

Broadly speaking, my invention produces a novel energizing signal for adeflection system, said signal comprising a composite waveform thatincludes a sinusoidal component and a pedestal component.

The following background information will aid in the understanding of myinvention. In FIG. 1, the desired variation of the deflecting signalwith respect to time is shown by the solid line waveform 10. Thiswaveform, generally known as a sawtoot waveform, comprises a rampportion 12 and a retrace portion 14. During ramp portion 12, thedeflecting signal is increasing, and therefore deflects the electronbeam progressively further from its starting point. The slope of rampportion 12 is a measure of how fast the electron beam is deflected,while the straightness, linearity, therefore is an indication of theabsence of compression or stretching. Retrace portion 14 repositions theelectron beam to its starting position. Since no display is drawn duringretrace, linearity is unimportant during this interval.

As previously discussed, prior art deflecting signals inherently departfrom linearity. This departure from linearity produces a curved shapedeflection signal known as an exponential, one form of which is shown bydotted line 16. As may be readily realized, the departure from linearityshown in FIG. 2 causes the final portions of the beam trace andtherefore the cathode ray tube display to be compressed. Prior artcompensating circuitry was designed to correct waveform 16 to thedesired waveform 12.

It was previously explained that an electrostatic deflection systemdepends on variations in voltage, whereas an electromagnetic deflectionsystem depends upon variations in current. Thus, in an electrostaticdeflection system, waveform represents the variation of the deflectingvoltage; whereas if the deflection system were of the electromagnetictype, waveform 10 would represent variations of the deflecting current.

In order to obtain the deflecting signal, an energizing waveform must beused. FIG. 2 shows a pedestal-type energizing waveform 18 which, whenimpressed across the deflection coils or the aforementioned capacitance,produces the nonlinear dotted line waveform 16 of FIG. 1. In the case ofelectrostatic deflection, waveform l8 represents a constant current thatflows through the capacitance, and produces a deflecting voltage;whereas in the case of an electromagnetic deflection system, waveform 18represents a constant voltage applied across the deflection coils, andproduces a deflecting current.

One way of obtaining the desired solid line deflecting signal 10 of FIG.1 with the linear ramp portion 12, is to use energizing waveform 20 ofFIG. 3, wherein the ramp portion 22 compensates for the undesirabledropping off characteristic 16 shown in FIG. 1. Unfortunately,production of the ramp portion of FIG. 3 is subject to the samenonlinearity problems as waveform 12 of FIG. 1. The waveform of FIG. 3therefore tends to be diflicult to produce.

I have found that a very close approximation of the desired waveform 10of FIG. 1 can be provided by using the energizing waveform 24 of FIG. 4.Waveform 24 comprises a sinusoidal component 25 superposed upon apedestal waveform component 27. Both of these components may be easilyproduced.

I produce composite waveform 24 by means of a sinusoidal Waveformgenerator, a pedestal waveform generator, and a circuit combining theoutputs of these two generators. While electron tubes may be used, Ihave found it most convenient to use the transistorized waveformgenerator shown in FIG. 5. In this circuit, the sinusoidal component 25is produced by the primary winding 26 of transformer 28 coacting withcapacitance 30 to form a resonant circuit. Transistor 32, which is shownas a PNP type, acts like a switch which supplies pulses of energy to theresonant circuit. When transistor 32 is nonconductive, as controlled bythe positive-going pulses of an input waveform 34, such as the one shownin FIG. 6, the resonant circuit oscillates and produces a series of sinewaves. The control waveform 34 may be produced by any suitablegenerator, for example, a suitably connected multivibrator (not shown).The duration of the positive pulses 35' is equal to the duration of onehorizontal line scan. However, the negative-going pulses 35" of controlwaveform 34 cause transistor 32 to conduct so that it shorts outcapacitance 30. This stops the oscillations, and the circuits outputappears as waveform 36 of FIG. 8. The ratio of turns between primarywinding 26 and secondary Winding 38 determines the amplitude of thesinusoidal component.

The pedestal waveform 27 of FIG. 4 is produced by a circuit comprising asecond transistor 40, whose state of conductivity is controlled by asecond input waveform 42 of FIG. 7, which is an inverted replica ofwaveform 34. The waveform 42 may be produced by the same generator whichproduces the waveform 34, it being only necessary to invert the waveform34. When transistor 40 is conductive, as controlled by thenegative-going pulses 43' of waveform 42, power source 47 produces aconstant potential across deflection coil 46, this corresponding to thedesired pedestal 27. This pedestal is also produced across the secondarywinding 38 of the transformer 28. The positive-going pulses 43" of thewaveform 42, corresponding to the retrace interval, keep transistor 40nonconducting.

Transformer 28 superposes the sinusoidal component 25, produced inwinding 26, onto the pedestal 27, produced in deflection coil 46 toproduce the composite volt age waveform 24; the short duration intervalsof waveforms 34 and 42 producing the retrace portion.

Deflection coil 46 inherently contains some resistance, and pedestal 27therefore produces an exponential current flow therethrough as shown bywaveform 41 of FIG. 9. Meanwhile, the sinusoidal component 25 causes thedeflection coil to experience the current flow shown by waveform 45 ofFIG. 9. This result can be shown mathematically, by consideringsinusoidal component 36 to be the portion of a sine wave between 270 and90, and therefore varying its unit value from --1 to +1. Since this is avoltage, the resultant current through the coil is the mathematicalderivative, and this is a cosine waveform varying between 27 and 90; itsunit value therefore changes from 0 to l, to 0. The resultant currentstherefore flow simultaneously through winding 38 dur ing the longinterval portions 35' and 43' of input waveforms 34 and 42. Properselection of the transformer turns ratio assures that the amplitude ofthe two components combine to form the straight ramp portion 44 of FIG.9.

The foregoing inventive concept has been explained in connection with anelectromagnetic deflection system where the energizing waveformsrepresent voltages, and the deflection signals represent current. Thesame inventive concept may be applied to electrostatic deflection,wherein the energizing and deflection Waveforms would represent currentand voltage respectively. Whereas FIG. 5 shows the use of PNPtransistors, it may at times be desirable to use NPN transistors. Thisis readily accomplished by reversing the polarity of the input signalsand the batteries.

It may thus be seen that my invention provides easily produced waveformsthat may be used to produce extremely linear deflection.

While I have described a preferred embodiment of the invention, it willbe understood that I wish to be limited not by the foregoingdescription, but solely by the claims granted to me.

What is claimed is:

1. A voltage deflection waveform generator for producing a deflectionwaveform having a scansion interval and a retrace interval forapplication to a deflection system comprising: means producing apedestal waveform; means energizing said pedestal waveform producingmeans for a duration equal to one scansion interval; means deenergizingsaid pedestal waveform producing means for a duration equal to saidretrace interval; means producing a sinusoidal waveform; meansenergizing said sinusoidal waveform producing means for a duration equalto one scansion interval; means deenergizing said sinusoidal waveformproducing means for a duration equal to one retrace interval; and meanscombining said waveforms, said combining means comprising a deflectioncoil.

2. A voltage deflection waveform generator for producing a deflectionwaveform for application to a deflection system, said deflectionwaveform having a scansion interval and a retrace interval, comprising:means producing a pedestal waveform; means energizing said pedestalwaveform producing means for a duration equal to one scansion interval;means deenergizing said pedestal waveform producing means for a durationequal to said retrace interval; means producing that portion of asinusoidal waveform between 270 electrical degrees and electricaldegrees on the normal sine wave curve; means energizing said sinusoidalwaveform producing means for a duration equal to one scansion interval;means deenergizing said sinusoidal waveform producing means for aduration equal to the retrace interval; and means combining saidwaveforms for the duration of said scansion interval.

3. A voltage deflection waveform generator for producing a deflectionwaveform for application to an electromagnetic deflection system, saiddeflection waveform having a scansion interval and a retrace interval,comprising; means producing a pedestal voltage waveform; meansenergizing said pedestal waveform producing means for a duration equalto one scansion interval; means deenergizing said pedestal waveformproducing means for a duration equal to the retrace interval; meansproducing the portion of a sinusoidal voltage waveform between 270electrical degrees and 90 electrical degrees on the normal sine wavecurve; means energizing said sinusoidal waveform producing means for aduration equal to one scansion interval; means deenergizing saidsinusoidal waveform producing means for a duration equal to the retraceinterval; means combining said waveforms, said combining meanscomprising a deflection coil; and means applying said composite voltagewaveform to said electromagnetic deflection system, whereby theresultant current in said system produces linear deflection.

4. In a deflection system having a scansion interval and a retraceinterval the combination comprising: a resonant circuit comprising aninductance and a capacitance, said resonant circuit having a resonantfrequency corresponding approximately to one half said interval, wherebysaid resonant circuit produces one half of a sinusoidal waveform duringa scansion interval; means shorting out said capacitance to render saidresonant circuit inoperative during said retrace interval, said shortingmeans comprising an electron conduction device; means producing apedestal waveform, a deflection means; means energizing said pedestalwaveform producing means for a duration equal to said interval, saidenergizing means comprising an electron conduction device, and means forcombining said Waveforms for application to said deflection means.

5. The combination comprising: a transformer having two windings; acapacitance connected in series with one of said windings whereby aseries resonant circuit is formed; a source of potential connected tosaid resonant circuit; a control device connected to said resonantcircuit whereby, according to the state of said device, said resonantcircuit is capable of producing a sinusoidal waveform of a predeterminedfrequency; a second circuit comprising the other winding of saidtransformer and a deflection coil; a source of potential connected tosaid second circuit; a second control device connected to said secondcircuit, whereby, according to the state of said second device, apedestal waveform having a duration equal approximately to one-half theinverse of said predetermined frequency is produced at said deflectioncoil; means controlling the states of said devices so that saidsinusoidal and pedestal waveforms are produced at the same time, wherebythe action of said transformer causes said Waveforms to be combined andimpressed on said deflection coil.

6. In a deflection system having a scansion interval of a predeterminedtime duration, the combination comprising: resonant circuit means, meansfor energizing said resonant circuit means to produce a substantiallysinusoidal waveform signal, the parameters of the elements of saidresonant circuit means being such that substantially only one half of acomplete sinusoidal waveform signal is produced during the predeterminedtime duration of each scansion interval, means for producing during saidscansion interval a pedestal waveform signal of a duration substantiallyequal to said scansion interval, and means for combining said pedestaland sinusoidal waveform si gnals produced during said scansion interval.

7. In a deflection system having a scansion interval of a predeterminedtime duration the combination comprising: a resonant circuit comprisingan inductance and a capacitance, means for energizing said resonantcircuit to produce a substantially sinusoidal waveform signal, theelements of said resonant circuit having parameters such so that thefrequency of said sinusoidal waveform signal corresponds substantiallyto one half the said predetermined time duration of said scansioninterval, means for producing a pedestal waveform signal ofsubstantially rectangular shape during said scansion interval, adeflection means, and means for combining a predetermined selectedportion of said sinusoidal waveform signal with each said pedestalwaveform signal for application to said deflection means.

References Cited in the file of this patent UNITED STATES PATENTS2,332,253 Peterson Oct. 19, 1943 2,479,081 Poch Aug. 16, 1949 2,496,283Gall Feb. 7, 1950 2,513,722 Harris July 4, 1950 2,562,305 Ellsworth etal July 31, 1951 2,659,837 Murdock Nov. 17, 1953 2,739,308 Lee Mar. 20,1956 2,911,566 Taylor Nov. 3, 1959 2,923,888 Buesing Feb. 2, 19602,933,641 Goodrich Apr. 19, 1960 2,962,664 Stryker et al Nov. 29, 1960

1. A VOLTAGE DEFLECTION WAVEFORM GENERATOR FOR PRODUCING A DEFLECTIONWAVEFORM HAVING A SCANSION INTERVAL AND A RETRACE INTERVAL FORAPPLICATION TO A DEFLECTION SYSTEM COMPRISING: MEANS PRODUCING APEDESTAL WAVEFORM; MEANS ENERGIZING SAID PEDESTAL WAVEFORM PRODUCINGMEANS FOR A DURATION EQUAL TO ONE SCANSION INTERVAL; MEANS DEENERGIZINGSAID PEDESTAL WAVEFORM PRODUCING MEANS FOR A DURATION EQUAL TO SAIDRETRACE INTERVAL; MEANS PRODUCING A SINUSOIDAL WAVEFORM; MEANSENERGIZING SAID SINUSOIDAL WAVEFORM PRODUCING MEANS FOR A DURATION EQUALTO ONE SCANSION INTERVAL; MEANS DEENERGIZING SAID SINUSOIDAL WAVEFORMPRODUCING MEANS FOR A DURATION EQUAL TO ONE RETRACE INTERVAL; AND MEANSCOMBINING SAID WAVEFORMS, SAID COMBINING MEANS COMPRISING A DEFLECTIONCOIL.